1. Technical Field
The invention relates to unions and couplings for pipes, tubing, and other fluid conduits.
2. Description of the Related Art
Many kinds of unions, couplings, and fittings have been designed in order to achieve fluidtight engagement of two or more pipe ends and other fluid conduits. Such couplings typically include at least two mated parts, male and female, which when connected form a fluidtight seal by compressing a sealing element such as an O-ring. Sometimes the mechanical complexity of a fitting results in a diminution of serviceability or convenience of use. It is important that a coupling permit quick-connect and disconnect, as well as maintaining seal integrity at the seal interface by preventing leakage of the fluid flowing through the piping.
When the conducted fluid is cryogenic in nature, the associated problems of seal integrity and usability of a coupling are compounded, due to the extremely low temperatures to which the seal and coupling elements are exposed. In particular, known couplings which primarily rely on transverse axial compression of a sealing element, such as a common O-ring, by tightening of a lug nut or similar means, have proven unsatisfactory because the cryogenic temperatures result in a loss of torque on the nut due to dimensional changes of the nut and its associated threaded shaft. Also, changes in characteristics of the sealing element, such as its resiliency, can occur at the low temperatures. When such changes result in a loss of the seal integrity, the cryogenic fluid quickly escapes the conduits and vaporizes; the fluid can also crystallize so as to block flow of the fluid in the piping or conduit with the result of having to shut down the equipment demanding the fluid flow and then reopening the fluid flow path.
In order to form and maintain a fluidtight seal, known devices have utilized high torque couplings and/or tight interface tolerances between the male and female mating surfaces and the sealing elements. One of the problems with using close tolerances on the mated parts is that assembly can be difficult in order to align the respective fluid passages in the mated male and female parts.
Self-aligning couplings are known and typical examples are shown in U.S. Pat. Nos. 655,088, issued to Kane, and 1,293,615, issued to Mitchell et al. These couplings are undesirable as they do not provide means for securely holding the pipe sections together, which is a necessity when using cryogenic fluids. These known couplings also do not prevent transverse movement or bending of the connected pipes at the coupling interface.
Other known types of couplings are shown in U.S. Pat. Nos. 2,971,782, issued to Sparkman et al., and 2,516,743, issued to Allin. While these devices provide, at least to some degree, a self-aligning coupling, they are deficient in that either they permit undesired transverse and longitudinal movement between the connected pipes or a coupling torque nut is needed to minimize such movement and effectuate the seal.